1. Field of the Invention
The invention generally relates to force measurement systems having a plurality of measurement surfaces. More particularly, the invention relates to a force measurement system with two or more measurement surfaces, which is particularly useful in the assessment of the balance of a subject.
2. Background and Description of Related Art
Force measurement systems are utilized in various fields to quantify the reaction forces and moments exchanged between a body and support surface. For example, in biomedical applications, force measurement systems are used for gait analysis, assessing balance and mobility, evaluating sports performance, and assessing ergonomics. In order to quantify the forces and moments resulting from the body disposed thereon, the force measurement system includes some type of force measurement device. Depending on the particular application, the force measurement device may take the form of a balance plate, force plate, jump plate, an instrumented treadmill, or some other device that is capable of quantifying the forces and moments exchanged between the body and the support surface.
A balance assessment of a human subject is frequently performed using a specialized type of a force plate, which is generally known as a balance plate. A balance plate is a sensitive weighing scale, which in addition to measuring the weight of the subject, also measures the point of application of the weight. Typically, this is achieved by having either three or four instrumented feet, each measuring the force transmitted through it. Then, based on how much force each foot carries, the point of application of the total force (i.e., the body weight is calculated). A typical use of a balance plate involves monitoring the manner in which this point of application of the force (i.e., the center of pressure) changes as the subject stands on the plate. For a quietly standing subject, the center of pressure variation is an indication of the amount of physiological sway that the subject experiences. Generally, a small center of pressure variation demonstrates that the subject is essentially stable, whereas a large center of pressure variation in quiet stance is interpreted as an indication that the subject may have difficulty maintaining his or her own balance, and may be in danger of sustaining a fall in normal daily living. Balance plates frequently are used in clinics and assisted-living environments by a clinicians and/or physical therapists who regularly carry the plate from one facility to another. Thus, it is highly desirable for a balance plate to readily portable.
During a balance assessment, if it is desired to make independent measurements under each foot of a subject, two balance plates are typically either placed side-by-side or mounted on a common base. This arrangement permits a determination of the weight that is carried by each leg of the subject, and if there is a deficiency in one of the legs. However, using two separate plates requires carrying additional hardware. Also, the operator has to make sure that the plates are not touching one another as the patient steps on and off the system so that an accurate measurement of each leg can be obtained. When two plates are mounted on one common base, the system becomes significantly heavier, and thus, more difficult to transport. Both conventional two plate systems also have the disadvantage that measurement from each plate is recorded independently, and poses not only an inconvenience, but also increases the possibility of inadvertently mixing the left and right signals.
Also, because many subjects that are tested on a balance plate have a balance disorder or a potential balance problem, it is very important that subjects are able to easily step on and off of the plate. Thus, it is highly desirable for the balance plate to have as low a profile as possible. Although, on a conventional balance plate, the force measuring feet are placed underneath the surface on which the patient stands, which increases the overall height of the instrument and consequently makes it more difficult for a patient having balance disorders to step on and off the plate.
What is needed, therefore, is a force measurement system that is in the form of a single force plate having two or more independent measurement surfaces for assessing the balance of a subject. Moreover, a force measurement system is needed that is readily portable, and thus, easy for an operator to transport from place to place. Furthermore, a need exists for a force measurement system that has a low profile so that it is easier for subjects, such as patients having balance disorders or potential balance problems to step on and off the apparatus.